Update documentation for PybelAssembler.to_web
Update documentation for PybelAssembler.to_web

- add documentation for return object
- add more information about how to use PyBEL configuration file to set defaults for variables

sorgerlab/belpy,bgyori/indra,bgyori/indra,sorgerlab/indra,bgyori/indra,johnbachman/indra,pvtodorov/indra,johnbachman/belpy,sorgerlab/belpy,pvtodorov/indra,sorgerlab/indra,sorgerlab/belpy,johnbachman/belpy,johnbachman/belpy,pvtodorov/indra,pvtodorov/indra,johnbachman/indra,johnbachman/indra,sorgerlab/indra